1. Field of the Invention
The invention pertains to a process for the preparation of 2-cyanoacetoxypropionic esters of the general formula III, in particular those having high optical purity, by reacting cyanoacetic esters I with lactic esters, in particular optically active lactic esters II, in the presence of a catalyst, with elimination of the alcohol radical from the cyanoacetic ester. ##STR1##
2. Description of the Related Art
Various processes are known from the literature for the preparation of III. Thus, EP-A 127,855 suggests, as a synthesis for III, the condensation of cyanoacetic acid with lactic esters with dehydration. Which chemical substances are required for this reaction, however, are not disclosed. In any case, expensive reagents are necessitated due to the fact that the dehydration must take place under gentle conditions, since otherwise high-boiling compounds are formed as the major product. This latter process is therefore relatively complex and uneconomical. A further problem is the thermal sensitivity of cyanoacetic acid. At slightly elevated temperatures, even below 100.degree. C., it begins to decompose and at still higher temperatures, this decomposition can take place explosively. Thus, safety problems are also a major disadvantage of this process.
Japanese Patent JP 84/222,461 discloses a somewhat similar process starting with cyanoacetic acid and reacting this with an .alpha.-chlorinated ester. In order to prepare 2-cyanoacetoxypropionic esters, the latter process would require the use of an .alpha.-chloropropionic ester: ##STR2## However, such .alpha.-chloropropionic esters are likewise unstable under the reaction conditions, so that in this synthesis pathway, both starting materials are unstable.
Commercialization is highly problematic given such conditions which, in summary, require expensive chemicals, deliver unsatisfactory yields and, moreover, also exhibit safety problems. A simple process is therefore desirable in which stable, easily accessible starting materials are used, for example esters, and in which these starting materials are reacted in the presence of a suitable catalyst without the use of additional reagents to give the target product.
The 2-cyanoacetoxypropionic ester products are important raw materials in the adhesives sector (see, for example EP-A 0,127,855) and in the pharmaceuticals field. Furthermore, for use as starting materials for pharmaceutical products, high optical purity is desirable, i.e., the optical activity which is introduced into the system by the use of optically active lactic esters must be maintained.